The conventional utility pole is wood and made from a tree trunk that has been processed to produce the customary lathed pole, generally cylindrical and of somewhat tapered shape. To this shaped trunk an impregnant and preservative is applied under pressure, to retard deterioration such as rot, decay and insect infestation. Conventionally, the preservative is creosote or an oil solution of pentachlorophenol and on application thereof, the wooden pole exhibits a life in excess of ten years under optimum conditions.
More often than not, optimum conditions do not prevail. The type of loading on the pole effects a shortening of its life. Indeed, wooden poles are severely limited in their load carrying capabilities because of their relatively low tensile, compressive and shear strengths when compared to metal poles and this is a severe limiting factor to expanding use of wooden poles.
Wooden poles exhibit other design limitations. For example, the voltages that can be safely carried near or on wooden poles is limited since the dielectric properties of wood vary with its relative wetness. Then too, certain environments mandate that the wooden poles be wrapped or jacketed in a fiberglass or resin jacket for added strength and prolonged life, which processes add to the cost of the finished product. Yet there is another factor detracting from further application of wooden poles impregnated, coated or otherwise treated. Competing uses of wood, a relatively limited natural resource, coupled with the relative shortage of wood generally, has caused the per se cost of same to soar. Hence, what was once an abundant and cheap source of structural material has come to be realized as a limited resource to be carefully conserved. Further, the rampant falling of living trees to make utility poles may adversely affect the ecological balance in a given area and so wood production has come under close scrutiny.
As an alternative structural material, it has been propounded to use metal, particularly aluminum. Yet this approach has several disadvantages, not the least of which is the enhancement of the probability of undesirable electrical phenomena associated with grounded and conductive supports contiguous to high voltage wire. And, metals generally are heavy and not inexpensive.